The present invention relates to an ultrasonic diagnostic apparatus and a driving method therefor, and particularly to an ultrasonic diagnostic apparatus comprising a probe having a larger number of transducers than the number of channels in transmitting/receiving means, and a driving method for such an apparatus.
Apparatuses for scanning a predefined region in a subject to be imaged by ultrasound to produce an image of the subject include the ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus is attracting attention because it can conduct a scan and produce an image without distressing the subject to be imaged.
The image produced by the ultrasonic diagnostic apparatus depends considerably upon the number of transmitting/receiving channels in the main body of the apparatus and the number of transducers in the probe. That is, the number of transmitting/receiving channels and the number of transducers are set to correspond to each other, and as the width of transducers becomes smaller and the number of transducers becomes larger, the density of scan lines increases, thus improving accuracy of the produced image. The transducers will be sometimes referred to as elements hereinbelow.
There have been developed probes of a linear or convex type that have elements arranged in a one-dimensional manner and have a large number of elements. On the contrary, in a transmitting/receiving circuit having channels for transmitting/receiving ultrasonic signals to/from the elements, the number of channels cannot easily be increased owing to limitation on the size etc. of the ultrasonic diagnostic apparatus. Therefore, a probe with 128–192 elements has been developed for a transmitting/receiving circuit with 32 or 48 channels, for example. In the ultrasonic diagnostic apparatus having such a probe, adjoining elements are connected to respective transmitting/receiving channels, and a linear or convex scan is achieved by sequentially moving the elements driven by the transmitting/receiving channels (see Non-Patent Document 1, for example).
In B-mode compounding in the linear or convex scan, however, driving consecutive elements as described above, hence narrowing an opening, may result in a broader main beam. Alternatively, driving with elements at certain spacings connected to transmitting/receiving channels to widen the area of the transmitting/receiving elements may result in grating lobes.
On the other hand, an active matrix array (sometimes referred to as AMA hereinbelow) probe in which elements are two-dimensionally arranged has been developed for an ultrasonic diagnostic apparatus having a transmitting/receiving circuit with 128 channels or more, although machines in widespread use generally employ a transmitting/receiving circuit with about 64 channels.
Furthermore, in a portable ultrasonic diagnostic apparatus, there is also a problem that the number of transmitting/receiving channels cannot easily be increased owing to size and/or weight considerations.
[non-Patent Document 1]“Handbook for Medical Ultrasonic Instruments,” edited by The Electronic Industries Association of Japan, published by Corona Publishing Co., Ltd., Revised Edition 1 (Jan. 20, 1997), page 94, FIG. 3.59; page 97, FIG. 3.64; and page 102, FIG. 3.76.